Multiregional hypothesis
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The multiregional origin hypothesis of human species holds that some, or all, of the genetic variation between the contemporary human races is attributable to genetic inheritance from either Homo sapiens subspecies, or even other hominid species, that were dispersed geographically throughout Asia, and possibly Europe and Australasia, prior to the evolution of modern Homo sapiens sapiens (conventionally dated to at least 70,000, possibly 150,000, years ago).
The contributing populations suggested by multi-regional hypothesis as sources for additional genetic variation in modern Homo sapiens include Homo neanderthalensis and Peking Man (a local subspecies of Homo erectus). This view contrasts with the single origin hypothesis, which holds that modern Homo sapiens evolved from a single, geographically localised, ancestral hominid population, whose descendants ultimately replaced all other species of hominids over the course of tens of thousands of years without interbreeding or subspeciation.
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Recent evidence
The multi-regional hypothesis was originally developed from the fossil evidence, but more recent work has focused on molecular data, in which DNA is sequenced. In particular, work has been done with non-recombining DNA such as mitochondrial DNA and the Y chromosome.
In 2001 a team of Chinese scientists wrote: "all Y-chromosome samples from China, with no exception, were originally derived from a lineage of African origin. Hence, we conclude that even a very minor contribution of in situ hominid origin in China cannot be supported by the Y-chromosome evidence." [1] In a related publication, scientists in Asia, the US, and the UK examined the Y-chromosomes of more than 12,000 people from across Asia and found no traces of any ancient non-African influence. [2]. This is of no surprise, because current understanding is that the earlier hominid species have originated also from Africa.
Nevertheless, proponents of multiregionalism such as Wolpoff believe the molecular data can not only be reconciled with the multiregional origin hypothesis but in fact in some cases supports it. For instance, studies on past population bottlenecks that can be inferred from molecular data have led them to conclude that the single-origin hypothesis is untenable. Discovery of a possible hybrid Homo sapiens X neanderthalensis fossil child at the Abrigo do Lagar Velho rock-shelter site in Portugal in 1999 raised hopes of rehabilitating the Multiregional hypothesis.
Recent, non-fossilized discovery of one metre tall, small brained (350 cc), Homo floresiensis, on Indonesian island of Flores, imply populations of Homo erectus survived very late, and gave rise to even later, physically smaller "Erectus" type isolated groups. The existence of Homo neanderthalensis, Late full sized Homo erectus, and now Homo floresiensis as contemporaries of modern Homo sapiens sapiens tends to refute the "serial development theory" on its face, and imply something of a more "parallel" development scenario.
Proponents of multiregionalism
Two of the scientists most closely associated with the multiregional hypothesis are Carleton S. Coon and Milford H. Wolpoff.
Wolpoff, however, distinguishes his own views from Coon's as follows:
- "Since its inception in the 1980s, multiregional evolution has never been polyphyletic. It has always been a theory about intraspecific evolutionary processes with an emphasis on gene flow... multiregional evolution [is not] a polyphyletic model of parallel racial evolution similar to that of Carleton Coon’s in the 1960s." [3]
However, Coon was explicit in the exposition of his theory that gene flow between populations played a substantial role in human evolution, a point often overlooked by his critics.
A variation of this theory known as hybrid-origin hypothesis was introduced in 1971 by the British psychologist Stan Gooch.
A recent Australian study of an ancient Aboriginal skeleton known as Mungo Man could be interpreted to support the multiregionalism hypothesis. The reasons for this is that genetic tests show the DNA of Mungo Man to be unrelated to those of modern man on the Mitichodrial line. Mungo man is an anatomically modern human and has been dated to be at least 40,000 years old. The study suggests that Mungo Man must have had a different direct ancestor on the female line to modern humans a branch that is now extinct. This tends to support the hybrid origin hypothesis.
Pre-modern (non-sapiens) hominids
Because of the scarcity of fossils and the discovery of important new finds every few years, researchers disagree about the details and sometimes even basic elements of human evolutionary history. While they have revised this history several times over the last decades, researchers currently agree that the oldest named species of the genus Homo, Homo habilis, evolved in Africa around two million years ago, and that members of the genus migrated "out of Africa" somewhat later. The descendants of these ancient migrants, which probably included Homo erectus, have become known through fossils uncovered far from Africa, such as those of "Peking man" and "Java man". The Homo neanderthalensis is also considered a descendant of early migrants.
Source: single origin hypothesis
See also
External links
- [4] - 'Genomics refutes an exclusively African origin of humans' (pdf) Vinayak Eswaran, Henry Harpending, Alan R. Rogers, Journal of Human Evolution (2005)
- [5] - 'Templeton tree'
- [6] - 'The Hybrid Child from Portugal'
- ActionBioscience.org - 'Origins of Modern Humans: Multiregional or Out of Africa?' (discoverer of 'Lucy' argues against multi-regionalism), Donald Johanson, American Institute of Biological Sciences (May, 2001)
- Biochem. Soc. Trans (2005) 33, 582-585 - J. Hardy and others - Molecular Mechanisms of Neurodegeneration (Evidence suggesting that Homo neanderthalensis contributed the H2 MAPT haplotype to Homo sapiens)
- Gene Expression - 'Population genetics notes' (only 1 migrant per generation between populations of any size can prevent divergence in allelic frequencies)
- Genetics - 'Deep Haplotype Divergence and Long-Range Linkage Disequilibrium at Xp21.1 Provide Evidence That Humans Descend From a Structured Ancestral Population' (first genetic evidence that statistically rejects the null hypothesis that our species descends from a single, historically panmictic population), Daniel Garrigan, Zahra Mobasher, Sarah B. Kingan, Jason A. Wilder, and Michael F. Hammer, University of Arizona, Tucson, Genetics, Vol. 170, 1849-1856, August 2005
- Linfield.edu - 'The Origin of Modern Humans: Multiregional and Replacement Theories', Michael Roberts, Linfield College
- OxfordJournals.org - 'Evidence for Archaic Asian Ancestry on the Human X Chromosome' (suggests ancient RRM2P4 lineage is remnant of introgressive hybrid of anatomically modern humans from Africa and archaic populations in Eurasia), Daniel Garrigan, Zahra Mobasher, Tesa Severson, Jason A. Wilder, Michael F. Hammer, University of Arizona, Tucson, Molecular Biology and Evolution, vol 22, no 2, p 189-192 (2005)
- PNAS.org - 'Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins', Gregory J. Adcock, Elizabeth S. Dennis, Simon Easteal, Gavin A. Huttley, Lars S. Jermiin, W. James Peacock, Alan Thorne, Australian National University, Proceedings of the National Academy of Sciences, vol 98, no 2, p 537-542 (January 16, 2001)
- StephenJayGould.org - 'Out of Africa vs. Multiregionalism', Tod Billings (December 7, 1999)
- TalkOrigins.org - 'The evolution of modern humans: where are we now?' Christopher B. Stringer, General Anthropology, vol 7, no 2, p 1-5 (2001)
![[5]](http://www.corante.com/loom/img/Templeton%20tree%20600.jpg){kind=link}